1. Field of the Invention
The present invention relates to an electronic level which automatically identifies or discriminates graduated numerical values marked on a collimated leveling rod (or staff), whereby a collimated position is obtained.
2. Description of the Related Art
As the above-described type of conventional electronic level, there has hitherto been known the following one in Japanese Published Unexamined Patent Application No. 272970/1993. Namely, the electronic level comprises: a telescope for collimating a leveling rod which has therein a graduation (or scale) pattern arranged at a predetermined pitch in a vertical (or longitudinal) direction of the leveling rod and also which has therein graduated numerical values of a single kind of size, the graduated numerical values being disposed corresponding to the graduation pattern; and a two-dimensional sensor for converting that image of the leveling rod which is collimated by the telescope to an image signal. The image signal is compared with an image data which are stored in advance to thereby discriminate or identify the graduated numerical values. The collimated position on the leveling rod is thus automatically computed.
In the above-described conventional electronic level, unless the following are attained, the measurement cannot be made. Namely, in order to specify or locate the positions of the graduation patterns and of the graduated numerical values in the image signals, a reference position must be set somewhere in the widthwise (or lateral) direction of the leveling rod. The collimation must then be made such that the reference position lies correctly in the center of field of view. Therefore, there are disadvantages in that much time is required for the collimation of the leveling rod and that the measurement results will become unstable due to interference or disturbance such as vibrations or the like.
In addition, in the above-described conventional electronic level, there are indicated graduated numerical values of only one kind of size. Therefore, if the distance between the telescope and the leveling rod becomes large, the graduated numerical value in the image signal becomes too small to be discriminated. On the other hand, if the graduated numerical values to be indicated on the leveling rod are made larger, there will be no problem in case the distance between the telescope and the leveling rod is large. However, in case the distance between the telescope and the leveling rod is small, the graduated numerical values will lie out of the field of scope, with the result that the graduated numerical values cannot be discriminated.